1. Field of the Invention
The present invention relates to a lead-free solder bump bonding structure, and is suitable when applied to a lead-free solder bump bonding structure that has, for example, a copper electrode (hereinafter, referred to as a Cu electrode) of a first electronic component and a Cu electrode of a second electronic component bonded by a lead-free solder bump.
2. Description of the Related Art
An example known technique of electrically connecting electronic components of an electronic device, etc., is to utilize a protrusion formed on an electrode and called a bump. In recent years, in view of environmental problems and the RoHS instruction (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) by EU, etc., bumps formed on Cu electrodes employ a lead-free solder alloy containing no Pb (see, for example, JP H05-50286 A).
Moreover, in accordance with the downsizing of electronic devices and the advancement of the high functionality thereof in recent years, high-density packaging is necessary in the field of semiconductor packaging. Hence, the flip-chip packaging technology advantageous for high-density packaging is becoming popular rapidly, and nowadays, a narrow pitch such that the electrode pitch is equal to or smaller than 200 [μm] is often required. According to such a narrow pitching, it is necessary to further miniaturize the bumps, while at the same time, the amount of current increases due to the advancement of the high functionality of chips in recent years.
In the bonded part of electronic components by a lead-free solder alloy (hereinafter, sometimes simply referred to as a lead-free solder bonded part), however, when a flowing current per a unit area (current density) increases, an electromigration of Cu at the lead-free solder bonded part (hereinafter, electromigration means the electromigration of Cu) occurs, resulting in a disconnection failure in some cases. Hence, in recent years, a lead-free solder bump bonding structure is proposed which has an Ni layer formed in advance on the Cu electrode of the lead-free solder bonded part, and causes Ni layer to function as a barrier layer in order to inhibit a Cu diffusion from the Cu electrode, thereby inhibiting an occurrence of an electromigration phenomenon even if the current density becomes high.
According to such a lead-free solder bump bonding structure employing the above-explained structure, however, in order to inhibit an occurrence of an electromigration, it is necessary to form the Ni layer as a barrier layer in advance on the Cu electrode surface prior to place a lead-free solder ball on the Cu electrode of a first electronic component, and to also form the Ni layer in advance on the Cu electrode of a second electronic component. Hence, the manufacturing process of the lead-free solder bump bonding structure becomes complex by what corresponds to the necessity of the Ni layer forming process, and thus the increase of the burden like the cost increase at the time of manufacturing is a technical disadvantage.
The present invention has been made in view of the above-explained circumstances, and it is an object of the present invention to provide a lead-free solder bump bonding structure which reduces a burden at the time of manufacturing in comparison with conventional technologies, and which can inhibit an occurrence of an electromigration phenomenon.